1. Field of the Invention
This invention relates to an optical unit switching apparatus for use in optical devices, such as fluorescence microscopes or phase contrast microscopes, in which optical units are switched from one type to another.
2. Description of the Related Art
In fluorescence microscopes, in general, light of a particular wavelength range as excitation light is applied to a sample, and fluorescence emitted from the sample and having a longer wavelength than the excitation light is observed. The structure of a fluorescence microscope will be described with reference to FIG. 1. Light emitted from a light source 18 advances on an optical path 16, and only a light component of a wavelength selected by an excitation filter 17 is passed therethrough.
The passed light is reflected to a microscope optical path 13 by a dichroic mirror 12 which has a characteristic for reflecting light of a short wavelength and passing light of a long wavelength. The reflected light excites a sample 15 through an objective lens 14, whereby fluorescence is emitted from the sample 15. The fluorescence passes the objective lens 14 and then the dichroic mirror 12. Extra excitation light is absorbed by a barrier filter 11, and only the fluorescence is converged on a plane 10 and observed. In general, the excitation filter 17, the dichroic mirror 12, and the barrier filter 11 are combined as a filter cassette 19. Such a filter cassette is prepared for each of reagents with different properties and selected by an optical unit switching apparatus in accordance with the purpose of observation.
Further, phase contrast microscopes are used to observe a sample which cannot be observed by bright field observation when there is no clear contrast in color or concentration between the sample and the ambience. Specifically, these microscopes convert phase information of the sample to an intensity difference, using light interference. The structure of a phase contrast microscope will be explained with reference to FIG. 2. At the front focus of a condenser lens 23, a ring slit 24 is formed to be annular with respect to an optical path 13 of the microscope. Light having passed the ring slit 24 illuminates a sample 22, and then converges on a phase ring 20 provided on the rear focal plane of an objective lens 21.
Light having passed the phase ring 20, whose phase is varied by a 1/4 wavelength, reaches a primary image plane 25. Further, light diffracted by the sample converges on the primary image plane 25 without being influenced by the phase ring 20, since it is distributed on the entire rear focal plane of the objective lens 21. Therefore, the light diffracted by the sample and the light having passed the phase ring 20, having a phase difference of 1/4 wavelength between them, interferes with each other, and the interference is observed as an intensity difference. Since the size of the ring slit 24 is determined from the numerical aperture of the objective lens 21, the ring slit member is selected in accordance with the type of the objective lens 21. The ring slit member is switched from one to another by means of an optical unit switching apparatus incorporated in the condenser. Accordingly, the conventional optical unit switching apparatus requires means for displaying the type of the optical unit mounted.
For example, in Japanese Utility Model Application KOKAI Publication No. 2-107109 (see FIG. 3), a type display member 47 indicates the types of optical units mounted on an optical unit switching apparatus main body 46, and a recess 48 is formed in the main body 46. One of the type display member 47 and the recess 48 is made of a magnet, and the other is made of a magnetic body. Therefore, the type display member 47 can easily be switched corresponding to the mounting and dismounting of the optical units. This means that the type of the optical unit presently positioned on the optical path 13, and the position of the optical unit to be used after switching can be recognized by relating the contents of a movable position display 45 indicative of an optical unit presently positioned on the optical path 13, to the contents of the type display member 47. From these two displays, however, the type of the optical unit presently positioned on the optical path 13, and the position of the optical unit to be used after switching cannot directly be recognized. In light of this, in Japanese Patent Application KOKAI Publication No. 8-338947 (see FIG. 4), a display portion 28a-28d is provided in front of each filter cassette, which is an optical unit. The display portion 28a-28d indicates the type of a filter incorporated in the filter cassette. In an operation surface of a fluorescent apparatus main body 26, apertures 27a-27g are formed such that the display portion 28a-28d can be exposed through the apertures 27a-27g in every position within a range in which a mountable filter cassette is movable. Accordingly, the display portions 28a-28d of all the mounted filter cassettes can be exposed through the apertures 27a-27g simply by mounting the filter cassettes in the fluorescent apparatus main body 26, so that the type of a filter cassette positioned in the microscope optical path 13, and the position of any other filter cassette to be used after switching can be recognized from one display. This means that the direction for the switching operation and the feeding amount can be directly recognized.
However, in a conventional fluorescence microscope using a light source of high luminance, leakage of light through the apertures is harmful. Thus, providing a fluorescence microscope with multiple apertures which are free from leakage of light inevitably complicates its structure. Further, such a switching mechanism is not applicable to a rotary type mechanism which is simple in structure and used in many optical unit switching apparatuses.